With the deregulation of telecommunications services, many countries are now seeing a proliferation of new operators providing both voice and data networks and who are in competition with the original `PTT` or monopoly operator. Typically, the original operator has an established mainly wired network while the new operators are introducing optical fibre networks based on synchronous (SDH or SONET) rings from the exchange or switch to a street cabinet serving subscribers. At the street cabinet, a synchronous multiplexer drops out 2 Mb/s channels which are further de-multiplexed to 64 kb/s voice and/or ISDN channels which are carried to the subscribers on twisted pair copper cables. Large, e.g. corporate users may be provided with their own optical circuit from the street cabinet.
The new operators have taken subscribers from the original operators by offering enhanced services and/or lower tariffs. This has encouraged the original operators to offer similar services and tariffs in an attempt to win back lost subscribers. The new operators are acutely aware of the potential loss of their newly acquired subscribers and are becoming increasingly concerned that any risk of loss of service should be minimised. It is believed that any such loss of service for a significant period of time will result in most of the subscribers reverting back to the original operator who will almost certainly have left in place their copper connections to the subscriber premises. This loss of service may for example result from a terrorist attack or from a fire damaging a switch beyond repair, or from major damage to the optical cables connected to a switch. Although there are various schemes for providing path protection in synchronous networks, these schemes do not address the problem of the catastrophic loss of a switch. There may also be a problem where engineers are excluded from a building containing equipment for a significant period of time, e.g. as the result of a fire or an explosion, and are thus unable to effect repairs. Thus, many of the new telecommunications operators are taking a keen interest in disaster recovery plans.
The current disaster recovery plan involves the provision of a replacement switch together with its associated transmission equipment and power generators, on vehicle trailers which can be towed to a disaster area and connected into the access network at a point remote from the damaged switch. A typical arrangement requires three large trailers together with a smaller back-up power trailer housing three 120 kvA generators. Such a set up is of course costly to maintain on a largely standby basis. Also, there may well be a significant delay before the equipment can be transported to the disaster area to initiate recovery of the network.